CNT research has been much progressed since its discovery and due to their versatile electrical, thermal and mechanical properties, and numerous applications have emerged for structural and electrical applications. Techniques like arc discharge, laser ablation and catalytic chemical vapor deposition (CVD) attempt to produce the CNT in the mass scale. CVD is considered to be the promising method due to low cost, ease of operation and tunable CNT growth control. It is well known that catalytic CVD process required the presence of the catalyst for the growth of CNT at the temperature range of 500° C. to 900° C. employing hydrocarbon feedstock. In this context, transitional metals of Group VIII metals such as iron, cobalt, and nickel are found to be effective in view of their ability in forming meta-stable carbide bond and high carbon solubility. However, the efficacy of these catalysts relies upon several parameters such as metal-promoters combination, metal dispersion, preparation method, and nature of oxide support and metal-support interaction.
U.S. Pat. No. 8,137,591B2 discloses the catalyst composition [FeaCobNic]p [MgxAlySiz]q for preparing carbon nanotube. The apparent density of CNT is disclosed as 0.03 to 0.08 g/cc and diameter of 5 to 20 nm. The disclosed catalyst composition comprises the employing of pre-synthesized nano-silicon powder with controlled particle size as one of the oxide supports. However, preparation of nano silicon powder is cumbersome as it involves the catalytic/high energy mechanical operation and therefore makes the catalyst expensive, and limits the catalyst scale up. Furthermore, low catalytic yields of CNT is disclosed, that is 1900% to 2400%, which is considered to be lower yields for process scale up.
U.S. Pat. No. 8,696,943B2 discloses the catalyst containing Fe and Co and at least one of the other elements consisting of Ti, V, Cr, and Mn; and a compound containing at least one element selected from the group consisting of W and Mo for CNT production. The catalysts described here are prepared by impregnation method, however low density multi-walled carbon nanotubes not disclosed employing of binary oxide supported catalysts. In addition, disclosed catalysts consist of iron, cobalt as the main metals along with promoters in the presence of oxide support carrier.
US20130171054A1 discloses the Fe, Co, and Mn supported catalyst for synthesizing multi-walled carbon nanotubes using gaseous hydrocarbon feedstock employing the catalyst composition, Fe:Co:Mn=1:x:y, wherein x and y are mole ratios and 2.0≤x≤4.0 and 0.01≤y≤5.0. The catalysts disclosed herein are prepared by incipient wetness impregnation supporting on aluminum oxide, magnesium oxide, silicon dioxide or a combination thereof in a solvent.
U.S. Pat. No. 9,084,990B2 discloses the multi-wall carbon nanotubes employing alumina and magnesium aluminate supported CoxFeyMoO4, Fe2(MoO4)3 and blends thereof, wherein the atomic ratio of magnesium oxide to alumina is about 0.02 to 0.04, wherein x and y for the mixed metal oxides represented by CoxFeyMoO4 is from about 1.6 to 6.5, and 0 to 10.5, respectively. However, this invention does not deal the selective catalyst composition for carbon nanotubes with controlled morphology with respect to density and tube diameter.
US20140072505A1 describes the production of helical carbon nanotubes along with another form of carbon nanotubes including single walled, double walled and multi-walled employing the layered multiphase catalysts prepared by impregnation and co-precipitation methods, wherein catalyst nanoparticles are reported to be located in the core or outer layers.
US20130039839A1 describes the production of carbon nanotubes with the bulk density of 130 g/liter with purity of 90 wt % employing co-precipitated catalysts, wherein the disclosed catalyst is pre-reduced at the temperature in the range of 300-900° C. before commencing the carbon nanotube production. The disclosed yield of carbon nanotubes is reported as 33.2 g/g-cat with the bulk density of 152 g/l.
US20090140215A1 discloses the CNT production with tube diameter of 3-150 nm and an aspect ratio greater than 100 employing the catalyst comprising cobalt, manganese supported on magnesia in an appropriate metal to support proportions. In this disclosure also, catalyst is pre-reduced for the CNT production.
EP2835177A1 discloses the method of producing the CNT using carbon black supported CoMn catalysts prepared by co-precipitation method employing urea as precipitating agent. However the metal-support interaction is weak in carbon supported catalysts, as a result low yields of CNT is reported.
U.S. Pat. No. 7,157,068B2 discloses the catalysts in gas phase employing organo metallic precursors namely metallocenes of iron, cobalt and nickel deposited on material substrate inside the reactor to produce non-aligned CNT of different morphology. The catalysts disclosed here is to generate metal nanoparticles upon heating condition and these species are responsible for the hydrocarbons decomposition. However, scaleup of the process is economically not viable due to high cost of metallocenes precursor for in-situ generation of the catalytic particles.
WO2014188439A1 describes the carbon dioxide free production of hydrogen and bamboo shaped carbon nanotubes by decomposition of lower hydrocarbons over the supported transitional catalysts based on Fe, Co and Ni in combination with Cu or Zn supported on alumina. The catalysts disclosed in this prior art are prepared by wet impregnation method, however CNT morphology with catalyst composition is not disclosed.
From the above prior art, it is evident that these processes are not viable for large-scale production based on their catalyst composition in particular for the tunable morphology of CNT. Moreover, selective production of CNT with variable morphology of bulk density and diameter on mass scale employing the binary oxide supported multi metal catalyst is yet to be unknown in the art. In this context, present invention disclosed the catalyst composition with active transitional metal in combination of structural and textural promoters for the production of CNT with controlled morphology.